Method and device for dosing a liquid preparation

ABSTRACT

A liquid preparation of a pharmaceutically active agent having a defined composation is repeatedly dosed from a multi-dose container having a defined volume. The amount dosed is selected as 1/N of the volume of the multi-dose container, N being an integer having a value of 2 or higher. 
     A device for dosing a liquid preparation comprises a holder (1) for a multi-dose container (2), which has a movable rear wall (5) acting as a piston for expelling the liquid preparation (6) from the container, and a piston rod (7), which is provided with releasable blocking means (11, 14, 19, 22), such that the movement of the piston rod is limited to a preset length (35) corresponding to an expelled volume of 1/N of the volume of said multi-dose container, N being an integer having a value of 2 or higher. 
     A preferred embodiment of the device is as an injection device for repeated parenteral injections from an injection cartridge.

The present invention is directed to the dosing of liquid preparations.More specifically, the invention refers to a method and a system for therepeated dosing of liquid pharmaceutical preparations which are to beadministered. Still more specifically, the invention refers to a methodand a system for the repeated dosing and administering of liquidpharmaceutical preparations by parenteral injection from a multi-dosecontainer. Furthermore, the invention also refers to a device forcarrying out the method of the invention, especially then in the form ofan injection device for repeatedly administering parenteral injectionsfrom an injection cartridge.

When a pharmaceutical agent is prescribed by a physician, the amount ordose to be administered to the patient is usually expressed inwell-known units, such as milliliters or international units (IU). Thedose is determined by such factors as the health status and weight ofthe patient, for example, and by rules from the health authorities. Inthose cases where the patient himself is to administer the doses, thephysician then selects a suitable multi-dose container, from which anumber of doses may be administered. Such a multi-dose container may bea vial, from which each individual dose is withdrawn by means of ahypodermic syringe, or it may be in the form of an injection cartridge,which is to be inserted in an injection device for repeatedadministrations. Injection cartridges have found a wide use because ofthe easiness in their handling and the diminished risk of infections,especially when the patient has to give himself repeatedadministrations. Injection devices in the shape of a pen for repeatedinjections of such preparations as, for example, insulin and growthhormones are commercially available. The user inserts an injectioncartridge in the device and attaches an injection needle to thecartridge, and the device is then ready for repeated injections. Thedevice may be set at different doses and is usually graduated in suchunits as milliliters or International Units.

It is usually desirable that the dose is set in such a way that therewill be a minimum residue of the preparation in the multi-dose containerafter a series of injections have been administered. This is of specialimportance when very expensive preparations are administered, such asgrowth hormones. This is not a problem when the multi-dose container isa vial from which the individual doses are withdrawn. If the remainingamount of preparation in the vial is insufficient for a complete dose,the user simply takes the missing amount from a fresh vial, and therewill be no unused residue.

However, this is not possible when an injection cartridge is used in aninjection device of a known type, and depending on the relation betweenthe prescribed dose and the contents of the cartridge, the residue maybe considerable. For instance, for a cartridge containing 12 I.U. of apreparation, only the doses of 1, 2, 3, 4, 6, and 12 I.U. will leave noresidue, but for other doses, there will be a considerable waste. Thus,for example, a dose of 4.5 I.U. will give a residue of 3 I.U. after twoadministrations, and a dose of 8 I.U. will give a residue of 4 I.U.after one administration. A dose of 6.25 I.U. will give a residue of5.75 I.U. after one administration, that is, nearly half of the contentsof the cartridge. For very expensive preparations, such as growthhormones, this is quite unacceptable.

It is not suitable for the user to give himself two injections toadminister the prescribed dose, as this will mean that a new dose valuehas to be set for the first injection from the second cartridge, and theprescribed dose value then reset. This may easily lead to errors in thecalculation and setting of the doses.

For expensive preparations, special dosage schemes have been tried,where the dose is varied from each administration to the subsequent one.This complicates the prescription for the physician, and may also leadto errors. Furthermore, this means that only the average dose will becorrect, and deviations will occur at each individual administration.This may lead to side effects.

By the method and the device of the invention, these disadvantages areeliminated. According to the present invention, a liquid preparation ofa pharmaceutically active agent is dosed by repeated administrationsfrom a multi-dose container having a defined volume, in such a way thatthe amount dosed is an integer fraction of the volume of the multi-dosecontainer. Expressed in another way, the amount dosed is selected as 1/Nof the volume of the multi-dose container, N being an integer having thevalue of 2 or higher. The concentration of the preparation in themulti-dose container is adapted to provide the desired dose.

The value of N is selected and set before the preparation is withdrawnfrom the multi-dose container, and is then maintained unchanged throughN successive injections, when said multi-dose container has beenemptied.

In a more preferred embodiment, the dosing is a series of N successiveparenteral injections from an injection cartridge.

To provide a suitable selection of doses to be administered by themethod of the invention, a series of multi-dose containers which containpreparations of different concentrations are provided. This will give awide range of combinations corresponding to varying doses. For instance,if four multi-dose containers with the concentrations A, B, C and D areused in an injection device wherein the contents of the container can bedivided into two, three and four equal parts, the following combinationsare possible:

    ______________________________________                                                 A    B           C      D                                            ______________________________________                                        2 parts    A/2    B/2         C/2  D/2                                        3 parts    A/3    B/3         C/3  D/3                                        4 parts    A/4    B/4         C/4  D/4                                        ______________________________________                                    

It is clear that with a greater number of denominators andconcentrations, the number of possible combinations becomes very great.

The greatest denominator (value of N) is determined by the number ofdays that the preparation can be stored, and by the number of doses perday. In one embodiment, wherein a growth hormone is administered, themaximum value of N is 21, when one dose is administered per day, and 42,when two doses are administered per day.

The smallest value of N is two, as this is the lowest value where amulti-dose container still exists. An N value of one means that thewhole contents of the injection cartridge is administered, and in thiscase, the method of the invention is of no interest.

The invention further refers to a device for repeated dosing of a liquidpreparation, comprising a holder device for a multi-dose container whichhas a defined volume and which contains a preparation having a definedcomposition. The multi-dose container is provided with a front wallwhich is fixed and through which may be arranged an outlet for thepreparation, and a movable rear wall, which may act as a piston to expelthe preparation through the outlet. In the holder device is alsoarranged a piston rod, by the action of which the rear movable wall maybe urged forward. What characterizes the device of the invention is thatthe piston rod is provided with releasable blocking means, by which theforward movement of said piston rod is limited to preset defined length,which corresponds to a forward movement of the movable rear wall for alength corresponding to 1/N of the volume of the multi-dose container, Nbeing an integer having a value of 2 or higher.

In a preferred embodiment of the device of the invention, the blockingmeans, after the piston rod and the rear movable wall have been movedforwards for the defined length, may be released from said piston rodand again be attached to it in such a position that the piston rod andthe rear movable wall may again be moved forwards for the same definedlength, and this process may be successively repeated until the pistonrod and the rear movable wall have been moved forwards N times, so thatthe multi-dose container is empty.

In a still further preferred embodiment, the device of the invention isarranged as an injection device for repeated parenteral injections froman injection cartridge.

In the drawings, an example of a preferred embodiment of a deviceaccording to the invention is shown. FIG. 1 shows the device before aninjection has been administered, and FIG. 2 shows the device after aninjection has been administered.

When a dose of a pharmaceutical preparation is to be set andsubsequently administered, the following steps are carried out.

1) The physician selects a suitable dose level against the background ofthe indication and the health status of the patient, directives from thehealth authorities and similar criteria.

2) The physician determines the weight of the patient, and with the aidof a table, a computer program, a nomogram or similar device determinesthe individual dose corresponding to the general dose level determinedunder step 1. Here, the physician will find information about whichconcentration of the preparation and which division of the multi-doseinjection cartridge are to be used in each specific case. It is to benoted that only one approximation has to be made, namely between theactual weight of the patient and the weight given in the table.

3) The injection device is set to the division of the multi-dosecartridge (the value of N) that is to be used. This setting may becarried out by the physician, by the pharmacist where the injectiondevice is bought, or by the patient himself on instructions from thephysician. The setting cannot then be changed easily. For the setting,the device may be made adjustable, or a device may be used, in which thesetting is fixed by the manufacturer of the device. In the latter case,a series of devices which are set to fixed values of N are provided, andthe physician or user selects one having a suitable setting.

4) When a dose is to be administered, the patient activates the blockingmeans of the injection device, such that the piston rod and the rearmovable wall of the multi-dose injection cartridge may be moved forwardfor the preset length and a defined fraction of the contents of thecartridge will be expelled and administered. When the next dose is to beadministered, the blocking means are released and activated anewcorresponding to the preset division of the injection cartridge. Whenthe preset number of doses have been administered, the cartridge isempty and may be exchanged for a fresh one, the initial setting stillbeing maintained.

The method and device of the present invention are intended for thedosing of liquid preparations of pharmaceutically active agents. Theexpression "liquid" is here to be given a wide interpretation, andincludes liquids of varying viscosities up to high viscosity values. Theliquid preparations may also be aqueous or non-aqueous solutions,emulsions or suspensions.

The method and device of the invention should not be confused with theprior art methods and devices for dosing and administering liquidpreparations. The prior art devices for repeated administration from amulti-dose cartridge usually consist of an injection device whichcomprises a mechanism for a stepwise movement forward of the rearmovable wall of the injection cartridge, such as a screw or ratchetmechanism. The steps which are possible with this type of mechanism arefixed and a dose can only be determined by a given number of steps.Thus, the mechanism may be adapted to the injection cartridge in such amanner that an advancement of the mechanism with one step will give adosed amount of, for example, 1/8 of the volume of the cartridge.However, the mechanism cannot then be easily adapted to give a dose of,for example, 1/7, 1/9 or 1/10 of the volume of the cartridge. This meansthat only a limited number of dose amounts are possible without giving aresidue.

In contrast to this, the dosing mechanism of the device of the inventionwill always give a dose which is 1/N of the volume of the cartridge,wherein N is an integer. The value of N is selected and set on thedevice before the series of administrations is started, and it cannotthen be easily changed. This means that when the set number of Nadministrations have been carried out, there will be no residueremaining in the cartridge. By providing a suitable range of cartridgeswith varying concentrations of the preparation and a suitable range ofvalues for N, it is possible to obtain a wide range of different doses.This range of doses may then be presented in a table, from a computermemory, or in a nomogram, for easy reference by the physician.

An embodiment of the device of the invention is shown schematically inthe drawing. In this embodiment, the device is an injection device forsetting and repeated administering of measured doses of a preparation byparenteral injections.

FIG. 1 shows a schematic sectional view of the device immediately beforean injection is to be administered. FIG. 2 shows the device after aninjection has been administered. In the figures, like parts have thesame reference numbers.

The device comprises a barrel 1, which at its front end is arranged toreceive an injection cartridge 2. The injection cartridge 2 has a frontfixed wall 3 wherein is arranged an injection cannula or needle 4, and arear movable wall 5, which acts as a piston, and is filled with aninjectable preparation 6. The injection cartridge and its arrangement inthe front end of the device are conventional, and need not be describedhere in more detail.

The rear movable wall 5 of the injection cartridge 2 is actuated by thepiston rod 7, the front end of which is resting against the rear face ofsaid movable wall 5. The piston rod is guided slidably through coaxialopenings in the transversal walls 8 and 9. These transversal walls aresolidly attached to the barrel 1, but at least one of these walls shouldbe displaceable for setting the dose, as will be described below.

Inside the barrel 1 and between the two transversal walls 8 and 9 arearranged the releasable blocking means for the piston rod 7. Theseconsist of a fixed front chuck 10 with jaws 11, which clamp around thepiston rod 7. The jaws are provided with inclined surfaces 12 aroundtheir outer circumference, and these inclined surfaces cooperate withcorrespondingly inclined surfaces 13 at the inner circumference of alocking ring 14, which is urged rearward by the action of a spring 15.The chuck 10 is secured to the front transversal wall by means of thecooperating sleeves 16 and 17, and the spring 15 is arranged undercompressive tension between the rear face of the transversal wall 8 andthe front face of the locking ring 14. Thus, the inclined surfaces 13 ofthe locking ring 14 are urged rearward against the inclined surfaces 12of the jaws 11 of the chuck 10, so that the jaws 11 are closed and willgrip the piston rod 7 securely. The grip may be released by moving thelocking ring 14 forward against the action of the spring 15.

The releasable blocking means further comprise a movable rear chuck 18,which is arranged to the rear of the front chuck 10. This rear chuck isof a similar construction as the front chuck 10, and has jaws 19, whichare provided with external inclined surfaces 20, which cooperate withcorrespondingly inclined internal surfaces 21 in a rear locking ring 22.This locking ring is urged forward by the spring 23. At its rear end,the chuck 18 is solidly attached to a circular washer 24 by means of thecooperating sleeves 25 and 26. The spring 23 is arranged undercompressive tension between the rear face of the locking ring 22 and thefront face of the washer 24, such that the locking ring 22 will be urgedforward and, through the cooperation between the inclined surfaces 20and 21, the jaws 19 of the rear chuck 18 will be closed around thepiston rod 7 and grip it securely. This grip may be released by movingthe locking ring 22 rearward against the pressure of the spring 23.

The locking ring 22 is provided with a peripheral flange 27, and aspring 28 is arranged between the rear face of the flange 27 and thefront face of the rear transversal wall 9, such that the spring 28strives to urge the locking ring 22 forward. As the jaws 19 of the rearchuck 18 are closed around the piston rod 7, however, and furthermore,the jaws 11 of the front chuck 10 are also closed around the piston rod,the locking ring 22 cannot be moved forward.

A yoke 30 is attached to the locking ring 22 at its edge rearward of theflange 27, and the arms of the yoke pass through holes 31 and may bepulled rearwards against the pressure of the springs 23 and 28, and willthen move the locking ring 22 rearward, so that the grip of the pistonrod 7 by the jaws 19 of the chuck 18 will be released. The movement ofthe yoke 30 is controlled by the rotation of the cam 32 around the shaft33. This shaft 33 is mounted between two brackets 34, which are integralwith the barrel 1 of the injection device. The cam 32 may be rotated bymeans of a handwheel or knob (not shown), which is attached to the shaft33.

In the position shown in FIG. 1, the device is ready for anadministration of an injection. The rear face of the washer 24 restsagainst the front face of the sleeve 29 of the rear transversal wall 9,and there is a spacing 35 between the rear faces of the locking ring 14and the front chuck 10 and the front faces of the locking ring 22 andthe rear chuck 18. It is this spacing 35 which determines the magnitudeof the dose to be administered.

FIG. 2 shows the device of the invention after an injection has beenadministered. The rear chuck 18 with its locking ring 22 and the washer24 have now been moved forward by the action of the spring 28, so thatthe front faces of the chuck 18 and its locking ring 22 rest against therear faces of the front chuck 10 and its locking ring 14. In itsmovement forward, the rear chuck has also gripped the piston rod 7 andbrought it forward and in its turn moved the rear movable wall 5 of theinjection cartridge 2 forward, to expel a dosed amount of thepreparation 6 through the needle 4.

There is now a spacing between the rear face of the washer 24 and thefront face of the sleeve 29, and this spacing is of the same magnitudeas the spacing 35 shown in FIG. 1.

The function of the device of the invention is as follows:

As stated previously, FIG. 1 shows the device ready for theadministering of an injection. The front chuck 10 grips the piston rod 7by means of the locking ring 14, which is urged rearward by the actionof the spring 15.

When the injection is to be administered, the front locking ring 14 ismoved forward a short distance sufficient to release the grip of thepiston rod 7 by the jaws 11 of the chuck 10. This may be achieved bymeans of, for example, an operating arm extending into the devicethrough an opening in the barrel 1 (not shown). Other embodiments ofthis function are apparent to those skilled in the art.

When the grip of the piston rod 7 by the front chuck 10 is released, thepiston rod will be moved forward by the action of the spring 28 on theflange 27 of the rear locking ring 22. As the jaws 19 of the rear chuck18 are held closed around the piston rod 7 by the action of the spring23 on the rear locking ring 22, this whole assembly will be movedforward by the spring 28, until the front face of the rear chuck 18 willabut the rear face of the front chuck 10. By this action, the piston rod7 will move the rear movable wall 5 of the injection cartridge 2 forwardfor a determined distance corresponding to the spacing 35, such that adetermined dose of the preparation 6 is expelled from the cartridge 2through the needle 4.

The yoke 30 will follow the rear locking ring 22 on its forwardmovement, and will not be hindered by the cam 32, as this cam ispointing forwards.

After the dose has been administered, the parts of the device are in thepositions shown in FIG. 2.

When a new dose is to be set for administration, the cam 32 is turnedaround its shaft 33 by means of a suitable handwheel or knob, which isnot shown. The movement of the cam 32 will then actuate the yoke 30 tomove it rearwards. This rearward movement will then also move the rearlocking ring 22 rearwards, such that the jaws 19 of the rear chuck 18are released around the piston rod 7. By the action of the spring 23 onthe front face of the washer 24, which is solidly connected with therear chuck 18, the whole assembly of washer 24, rear chuck 18, spring 23and rear locking ring 22 will be moved rearwards until the rear face ofthe washer 24 abuts the front face of the sleeve 29 of the reartransversal wall 9. During this rearward movement, the piston rod 7 iskept stationary by the clamping action of the front chuck 10.

When the rear chuck 18 and the washer 24 have been moved the fulldistance rearwards, there is again a spacing 35 between the front facesof the rear chuck 18 and its locking ring 22 and the rear faces of thefront chuck 10 and its locking ring 14. This spacing 35 corresponds tothe dose set.

When the cam 32 has been rotated half a revolution, such that it ispointing rearwards and the yoke 30 is in its most rearward position,this position corresponds to a position of the rear locking ring 22 thatis somewhat further rearwards than what corresponds to the washer 24abutting against the front face of the sleeve 29. On further turning ofthe cam 32, the yoke 30 and the rear locking ring 22 will be movedsomewhat forward by the action of the spring 23, so that the jaws 19 ofthe rear chuck 18 will lock securely around the piston rod 7 in its newposition.

During this rearward movement, the spring 28 has also been cocked, andis ready to deliver a new injection. This feature gives the deviceauto-injecting properties, and there is no need for the user to exertany force for expelling the set dose of the injectable preparation 6from the injection cartridge 2 through the needle 4.

The device is now as shown in FIG. 1, and is ready to administer a newdose. These setting and administering steps are repeated according tothe injections prescribed by the physician until the injection cartridgehas been emptied. The cartridge may then be removed and a freshcartridge inserted.

In the embodiment of the device shown in the figures, the front chuck 10is fixed to the transversal wall 8, while the rear chuck 18 is movableforwards and rearwards for the administering of a dose and the settingof a new dose for administration. However, it is also possible toarrange the fixed chuck to the rear of the movable chuck. The barrel 1will then be provided with stopping means extending from its internalwall for stopping the forward movement of the movable chuck after apredetermined distance. The modifications necessary for this embodimentare within the competence of a person skilled in the art.

Before a fresh cartridge is inserted, the piston rod 7 should be movedback to its rearmost starting position. This may be achieved byreleasing both chucks 10 and 18, and this may be arranged by inserting asuitable tool (not shown) through an opening in the wall of the barrel1, such that the two locking rings 14 and 22 are moved forwards andrearwards, respectively, to release their grip around the jaws 11 and19, respectively. The fresh cartridge may then be inserted, for instanceby unscrewing a front portion of the barrel 1 from a rear portionthereof, so that the compartment for the cartridge becomes accessible.

The device of the invention is suitable for single-chamber as well asdual-chamber injection cartridges. Such cartridges are of a conventionalcharacter, and their design and readying for use need not be describedhere in more detail.

When the piston rod 7 has been moved back to its rearmost startingposition, its front end should still protrude from the front transversalwall 8 for a given distance. When a single-chamber cartridge is used,this distance should be such that the front end of the piston rod willrest against the rear movable wall 5 of the injection cartridge whensaid cartridge has been put in its correct position and the injectiondevice has been assembled and readied for use, such as by screwing thefront and rear parts of the barrel 1 together. When a dual-chamberinjection cartridge is used, the protruding length of the piston rod 7should be such that when the cartridge has been put in its position andthe device is screwed together, the front end of the piston rod 7 willpush the rear movable wall 5 of the cartridge forward, such that the twocomponents in the two chambers of the cartridge will be combined andmixed in the conventional way during the assembly of the device. Theappropriate length of the piston rod 7 can easily be determined by aperson skilled in the art.

The magnitude of the dose set to be administered is determined by thespacing 35 between the two locking rings 14 and 22 or between the washer24 and the front face of the sleeve 29 of the rear transversal wall 9.This spacing 35 may be set by varying the distance between the front andrear transversal walls 8 and 9. Thus, at least one of these transversalwalls 8 and 9 should be arranged to be displaced for a set distance, andit is preferred that the rear transversal wall 9 is movable, as thiswill not change the distance that the piston rod 7 will protrude fromthe front transversal wall 8 when said piston rod is in its startingposition. The setting of the distance between the two transversal walls8 and 9 may be carried out by the physician or the pharmacist by meansof special tools, and this setting should then not be easily changedafterwards. In this way, it is assured that the patient will always getthe same, predetermined dose.

As has been stated in the foregoing, it is an essential feature of theinvention that the dose set is always 1/N of the volume of the injectioncartridge, N being an integer having a value of 2 or higher. In thisway, it is assured that there will be no residue of the injectablepreparation when the determined number of doses have been administered.As the injection cartridge is cylindrical, a set dose will berepresented as a determined distance of movement for the rear movablewall 5 of the cartridge, and the correct setting may be made with thehelp of a suitable scale, or the like.

The injection device of the invention shown above is especially adaptedto the process of the invention, as the setting of the dose to beadministered can be made continuous and not stepwise, as in the priorart processes and devices. In combination with a range of differentconcentrations of an injectable preparation in different injectioncartridges, it has thus become possible to provide an injection systemwhich gives the correct dose of preparation to the patient and at thesame time does not leave a residue of the preparation, so that costlywaste of the preparation is eliminated.

In the present specification, the device of the invention has beendescribed with reference to a specific example shown in the drawingfigures. It is to be noted, however, that the embodiment shown is onlyan example, and that other embodiments and variants of the invention arepossible within the scope of the appended claims.

Furthermore, it is to be noted that although the invention has beendescribed in detail with reference to the most preferred embodiment,i.e. a method and device for the administration of parenteral injectionsfrom an injection cartridge, this is not the only possible applicationof the invention. It is also possible to employ the method and device ofthe invention for the administration of pharmaceutical agents by otherroutes of administration than parenteral injections, such asintranasally, intraocularly, topically, rectally and otiticadministration. The injection needle will then be replaced by some otheradministering means, and other modifications of the device may benecessary, as is apparent to those skilled in the art.

We claim:
 1. A method for the repeated dosing of a liquid preparation ofa pharmaceutically active agent to provide doses of a desired magnitude,by administration from a multi-dose container having a defined volume,said container having a fixed front wall through which is arranged anoutlet for said preparation and a rear movable wall acting as a pistonfor expelling said preparation through said outlet by means of themovement of a piston rod connected to a dosing mechanism, and comprisingthe steps of:a) defining a dose level of the pharmaceutically activeagent adapted for unchanged but repeated administration to a patient; b)selecting combination of (i) a concentration of the pharmaceuticallyactive agent in the liquid preparation contained in the multi-dosecontainer and (ii) a partial volume of said liquid preparation, whichpartial volume is 1/N of said defined volume of the multi-dosecontainer, N being an integer having a value of 2 or higher, thecombination of (i) and (ii) giving the dose level defined under a); c)connecting a multi-dose container, containing the defined volume ofliquid preparation of said concentration, to the piston rod and dosingmechanism; and d) performing exactly N individual and successiveadministration strokes with the piston rod, each stroke affecting therear movable wall to expel an equal volume of the liquid preparation ineach stroke, said volume being said partial volume; whereby thecontainer is emptied after the N successive administration strokes.
 2. Amethod according to claim 1, characterized in that said multi-dosecontainer is an injection cartridge for parenteral injection.
 3. Amethod according to claim 2, characterized in that the concentration ofsaid liquid preparation in said multi-dose container is adapted toprovide the desired dose.
 4. A method according to claim 2,characterized in that N is an integer between 2 and
 42. 5. A methodaccording to claim 4, characterized in that the concentration of saidliquid preparation in said multi-dose container is adapted to providethe desired dose.
 6. A method according to claim 1, characterized inthat the concentration of said liquid preparation in said multi-dosecontainer is adapted to provide the desired dose.
 7. A method accordingto claim 1, wherein the pharmaceutically active agent comprises growthhormones.
 8. A device for repeated dosing of a liquid preparation of apharmaceutically active agent, comprising a holder device for amulti-dose container having a defined volume and containing apreparation having a defined composition, said container having a fixedfront wall through which is arranged an outlet for the preparation and arear movable wall acting as a piston for expelling said preparationthrough said outlet, and a piston rod, by which the rear movable wallmay be urged forwards, wherein the improvement comprises:a) a movablechuck adapted to clamp around the piston rod under the action of aspring force, said clamping action being releasable by reducing saidspring force; b) jaws in said movable chuck having inclined surfaces andcooperating with locking means for closing the jaws and gripping thepiston rod; c) a yoke arrangement by means of which said movable chuckmay be released and moved rearward along said piston rod; and d) atleast one wall limiting the motion of said movable chuck, the wall beingdisplaceable for setting the dose.
 9. A device according to claim 8,characterized in that said blocking means, after the piston rod and therear movable wall have been moved forward for said defined length, maybe released from said piston rod and again be attached to it in such aposition that said piston rod and said rear movable wall may again bemoved forwards the same defined length, and this process may be repeatedsuccessively until the piston rod and the rear movable wall have beenmoved forwards N times, so that said multi-dose container is empty. 10.A device according to claim 9, characterized in that it is arranged asan injection device for repeated parenteral injections from an injectioncartridge.
 11. A device according to claim 8, characterized in that itis arranged as an injection device for repeated parenteral injectionsfrom an injection cartridge.
 12. A device according to claim 11,characterized in that it comprises a barrel for holding at its front endan injection cartridge and a piston rod for actuating said injectioncartridge for expelling a set amount of an injectable preparation fromsaid cartridge, characterized in that said releasable blocking meanscomprise a fixed chuck and a movable chuck which clamp around the pistonrod under the action of a spring force, said clamping action beingreleasable by reducing said spring force, and that said device furthercomprises a yoke arrangement, by means of which said movable chuck maybe released and moved rearward along said piston rod, while at the sametime cocking a spring when said movable chuck is again clamped aroundthe piston rod, and means for releasing said fixed chuck, whereby saidmovable chuck and said piston rod may be moved forward by the action ofsaid cocked spring, the distance that said movable chuck moves forwarddetermining the magnitude of the dose set.
 13. A device according toclaim 12, characterized in that said injection cartridge is of thesingle-chamber type.
 14. A device according to claim 12, characterizedin that said injection cartridge is of the dual-chamber type.
 15. Adevice according to claim 11, characterized in that said injectioncartridge is of the single-chamber type.
 16. A device according to claim11, characterized in that said injection cartridge is of thedual-chamber type.